Crystallizer is a versatile and modern chemical processing equipment in the industry for separating liquid-solid materials. This equipment is used in chemical process industries (CPI) to produce high-purity products from solutions containing impurities with relatively low energy input. It has the ability to recycle various chemicals like PET material to change state from semi-crystalline to amorphous material. The crystallizer process is generally known as crystallization which can be done as a continuous or a batch process in this equipment.
Crystallization helps to generate solid material from the liquid or gaseous phase. The crystal of soluble substance can be achieved from a hot saturated solution and separating the soluble solid from the solution through this technique.
It has the ability to remove liquid wastes from the discharge material completely, resulting in no liquid discharge (ZLD). The first crystal formation through this technique is known as primary nucleation. Then secondary nucleation occurs which generates a large production of crystals. The process of this technique occurs through the evaporative crystallization and cooling crystallization process.
Crystallizer Working Principle
The working activities of the crystallizer are associated with the controlled formation of crystals from a solution or liquid phase state. The solution in the cooling crystallizer is gradually cooled and the solubility power of the solute becomes decrease which helps to form a crystal. The solvent is evaporated and crystal nucleation occurs. The process should be controlled carefully to get good crystal material. This equipment uses definite temperature, cooling/heating coils, agitation, and separation technique to produce high-purity crystal products.
The process of crystallization occurs mainly in two steps known as nucleation and crystal growth. The solute molecules are getting together into clusters, on the microscopic scale after increasing the solute concentration which leads to forming stable crystal nuclei. Then the growth of the crystal structure of the molecule can occur where the molecules or atoms of solute precipitate out of the solution, and dissolve back into the solution in a dynamic condition.
Parts of Crystallizer
It consists of the following essential parts:
Vessel Body: This part of the crystallizer contains the solution or liquid undergoing crystallization. The vessel body is constructed based on the required temperature and pressure conditions to produce targeted products.
Agitator/Mixer: This part helps to maintain uniformity and prevent settling or agglomeration of crystal products. It produces efficient heat and mass transfer to the formation of crystal growth.
Cooling/Heating Coils or Jackets: This essential part helps to control the temperature of the solution within the vessel body. Cooling coils help to facilitate cooling crystallization and while heating coils or jackets leads to an evaporative crystallization process.
Nucleation Control Devices: These parts control the formation of nuclei which is very important to determine crystal size and uniformity.
Crystal Separator: This part helps to remove crystals from the mother liquor after the crystallization process is completed.
Feed Inlet: This part allows the feed introduction of the solution.
Discharge Outlet: This part is used to collect the crystals or the concentrated solution.
Level and Temperature Sensors: These devices are used for monitoring and controlling the level and temperature of the solution in this equipment.
Sight Glass or Viewing Port: This part helps with visual inspection of the progress of crystallization and the crystal bed inside the vessel.
Insulation: This part prevents the loss of heat by maintaining the desired temperature conditions. The vessel body of the crystallizer is kept in insulated conditions.
Pressure Relief Valves: This part prevents over-pressure on this equipment and ensures safety.
Crystallizer Types
There are mainly three types of crystallizer presence based on their specific applications and requirements which are given below:
Batch Crystallizer: It contains only a single vessel. The operation process of this equipment is very easy and suitable for small-scale productions.
Continuous Crystallizer: It is suitable for large-scale production. There exist many types of continuous crystallizers such as the draft tube baffle crystallizer, the mixed-suspension mixed-product removal crystallizer, and the fluidized bed crystallizer.
Forced circulation crystallizer: This type of crystallizer circulates the solution in the vessel body quickly. It controls the crystal size to increase the faster nucleation process.
Requirements for the selection of a proper crystallizer
It is very essential to select an effective crystallizer to get good products. This task depends upon the raw material availability, the properties of the system, and customer choices. The basic requirements are given below to select the good crystallizer equipment:
Step 1: Specify the requirements
You should first determine the goal to design this equipment to produce your final products including desired crystal size, purity matter, production rate facilities, and the best operating conditions. You should also remember the space availability, cooling capacity, and solute solubility curve to get the best production facilities.
Step 2: Calculate the requirements of heat transfer abilities
You must calculate the heat transfer rate for cooling the solution to the desired crystallization temperature by following the formula:
H = m × Cp × ΔT
Where,
H = Heat transfer required (J)
m = Mass of the raw solution (kg)
Cp = Specific heat of the solution ( J/kg·°C)
ΔT = Temperature differences ( °C)
Step 3: Calculate the Cooling Area
You must calculate the cooling area by following the formula:
C = Q / U × ΔTlm
Where,
C = Cooling area (m²)
U = The heat transfer coefficient (W/m²·°C)
ΔTlm = Logarithmic mean of the temperature difference in the cooling area ( °C)
Step 4: Evaluate the requirements for agitation
You must evaluate the requirements for agitation to understand the uniform mixing and prevent crystal agglomeration during the crystallization process.
Step 5: Choose the type of crystallizer and configuration style
It should choose the appropriate crystallizer and its configuration based on the cooling area, agitation requirements, and other factors needed.
Step 6: Considering the nucleation control
It should consider the controlling of crystal nucleation and uniformity and install the nucleation-promoting devices.
Step 7: Determine the separation technique
It should consider the separation technique like filtration, centrifugation, etc for removing the crystals from the mother liquor after crystallization.
Step 8: Finalize the design of the crystallizer
It should finalize the dimensions of this equipment, heating/cooling, agitation system, and various operational parameters based on the calculations and design considerations.
Step 9: Building the crystallizer based on your identifications
Construct the selected crystallizer based on your identifications and test its performance with sample solutions for verifying the desired objectives and requirements of our needs.
Crystallizer Applications
There are numerous uses for this equipment in the chemical process industry. Some uses of this equipment are given below:
Food and Beverage: This equipment has a versatile use in the production of salt, sugar, chocolate, and various food items to increase their taste, texture, and appearance.
Chemical Engineering: It is crucial equipment in the chemical process industry for the separation and generation of high-purity substances, and recovering valuable products from waste streams.
Pharmaceuticals: This equipment is essential in the field of pharmaceuticals to get high-purity drug crystals. It is very effective in the production of high-quality antibiotics, various types of vitamins, and various active pharmaceutical ingredients (APIs).
Petrochemicals: It is very helpful equipment for the purification and processing of various petrochemical products like fatty acids, paraffin wax, soap, detergent, and various products.
Mining and Minerals: This equipment is essential to extract valuable metals from ore like copper, nickel, and uranium.
References
1.Beckmann, W. (Ed.). (2013). Crystallization: basic concepts and industrial applications. John Wiley & Sons.
2. Chianese, A., & Kramer, H. J. (Eds.). (2012). Industrial crystallization process monitoring and control. John Wiley & Sons.
